ipcs(1)ipcs(1)Nameipcs - report interprocess communication facilities status
The command provides information about active, interprocess communica‐
tion facilities, message queues, shared memory, and semaphores that are
currently active in the system.
The information is displayed in columns and is controlled by the fol‐
-m Displays information about active shared memory segments
-q Displays information about active message queues
-s Displays information about active semaphores
If any of the options -q, -m, or -s are specified, information about
only those indicated are printed. If none of these three is specified,
information about all three are printed.
-a Uses all print options (shorthand notation for -b, -c, -o, -p
-b Displays the biggest allowable size information (maximum number
of bytes in messages on queue for message queues, size of seg‐
ments for shared memory, and number of semaphores in each set
-C Uses the specified core file (next argument) in place of
-c Displays creator's login name and group name
-N Uses the specified namelist (next argument) in place of
-o Displays the outstanding usage information (number of messages
in queue, size of each and number of processes attached to
shared memory segments)
-p Displays the process ID information (process ID of last process
to send a message and process ID of last process to receive a
message on message queues and process ID of creating process and
process ID of last process to attach or detach on shared memory
-t Displays all time statistics (time of the last control operation
that changed the access permissions for all facilities, time of
last and last on message queues, last and last on shared memory,
last on semaphores)
The column headings and the meaning of the columns in an listing are
given below. The letters in parentheses indicate the options that
cause the corresponding heading to appear; all means that the heading
always appears. Note that these options only determine what informa‐
tion is provided for each facility; they do not determine which facili‐
ties are listed.
T (all) Type of facility:
q Message queue
m Shared memory segment
ID (all) The identifier for the facility entry.
KEY (all) The key used as an argument to or to create the
facility entry. Note: The key of a shared memory
segment is changed to IPC_PRIVATE when the segment
has been removed until all processes attached to
the segment detach it.
MODE (all) The facility access modes and flags.
The mode consists of 11 characters. The first two
characters are interpreted as follows:
R If the process is waiting on a
S If a process is waiting on a
D If the associated shared memory segment has
been removed. It disappears when the last
process attached to the segment detaches it.
C If the associated shared memory segment is
to be clear when the first attach is exe‐
- If the corresponding special flag is not
The next 9 characters are interpreted as three sets
of three bits each. The first set refers to the
owner's permissions; the next, to permissions of
others in the user-group of the facility entry; and
the last to all others. Within each set, the first
character indicates permission to write or alter
the facility entry, and the last character is cur‐
The permissions are indicated as follows:
r If read permission is granted
w If write permission is granted
a If alter permission is granted
- If the indicated permission is not granted
OWNER (all) The login name of the owner of the facility entry.
GROUP (all) The group name of the group of the owner of the
CREATOR (a,c) The login name of the creator of the facility
CGROUP (a,c) The group name of the group of the creator of the
CBYTES (a,o) The number of bytes in messages currently outstand‐
ing on the associated message queue.
QNUM (a,o) The number of messages currently outstanding on the
associated message queue.
QBYTES (a,b) The maximum number of bytes allowed in messages
outstanding on the associated message queue.
LSPID (a,p) The process ID of the last process to send a mes‐
sage to the associated queue.
LRPID (a,p) The process ID of the last process to receive a
message from the associated queue.
STIME (a,t) The time the last message was sent to the associ‐
RTIME (a,t) The time the last message was received from the
CTIME (a,t) The time the associated entry was created or
NATTCH (a,o) The number of processes attached to the associated
shared memory segment.
SEGSZ (a,b) The size of the associated shared memory segment.
CPID (a,p) The process ID of the creator of the shared memory
LPID (a,p) The process ID of the last process to attach or
detach the shared memory segment.
ATIME (a,t) The time the last attach was completed to the asso‐
ciated shared memory segment.
DTIME (a,t) The time the last detach was completed on the asso‐
ciated shared memory segment.
NSEMS (a,b) The number of semaphores in the set associated with
the semaphore entry.
OTIME (a,t) The time the last semaphore operation was completed
on the set associated with the semaphore entry.
Things can change while is running. The picture it gives is only a
close approximation to reality.
/vmunix system namelist
/etc/passwd user names
/etc/group group names
See Alsoipcrm(2), msgop(2), semop(2), shmop(2)ipcs(1)